DE102018133282A1 - Method for monitoring the temperature of a motor winding - Google Patents

Abstract

The invention relates to an electric motor with a stator (1) with motor windings (2) and with a temperature monitoring device (10) for monitoring the temperature of at least one motor winding, the temperature monitoring device (10) having a measuring line (20) in the area of the motor winding, which is extends from a connection (21) for coupling an electromagnetic pulse or signal to a measuring line end (22), the temperature monitoring device (10) having a signal generating device (30) for generating an electromagnetic pulse or signal and a measuring device (40) for measuring the Signal transit time in the measuring line (20), and an evaluation unit (50), which is designed to determine the current temperature of the motor winding from the signal transit time currently being recorded.

Description

The invention relates to an electric motor with a temperature monitoring device and a method for monitoring the temperature of a motor winding of an electric motor.

There are various sensor-based solutions in the prior art for monitoring the motor temperature or the temperature of the motor windings. Known methods or measures are the use of thermal sensors, Kalman filters, sensors or by means of mathematical models.

When using sensors such as thermal switches or thermal sensors, which measure the temperature in particular on the windings of the electric motor, the temperature is only recorded locally on the one hand and there is an assembly effort to mount the sensors at a suitable point. In order to enable efficient temperature monitoring, it is known to calculate a temperature distribution from the point-by-point temperature values using thermal models. However, this sometimes requires high computing power and process processing, making the hardware required for the calculations expensive and taking up a lot of space. In addition, the thermal models, on the basis of which the temperature distribution is calculated, can be faulty and mostly cannot be adapted to changes in the conditions and are sometimes not adaptable. For example, a calculated temperature distribution can deviate from the actual temperature distribution due to wear or through maintenance measures.

Another disadvantage of various methods known in the prior art using sensors and thermal switches lies in the technically-related aging and accordingly in a limited service life.

It would therefore be desirable to have a solution that is inexpensive to implement, requires little installation space, has a long service life with constant conditions and reliably enables temperature detection.

It is therefore an object of the present invention to provide a temperature monitoring device which is simplified and inexpensive to implement compared to the prior art, and a method for monitoring motor winding temperatures.

This object is achieved by the combination of features according to claim 1.

According to the invention, an electric motor with a stator with motor windings and with a temperature monitoring device for monitoring the temperature of at least one motor winding is proposed, the temperature monitoring device having an (insulated) measuring line in the area of the motor winding, which extends from a connection for coupling an electromagnetic pulse or signal to extends to a measuring line end, the temperature monitoring device having a signal generating device for generating an electromagnetic pulse or signal and having a measuring device for measuring the signal transit time in the measuring line and an evaluation unit which is designed from the currently recorded signal transit time (pulse transit time) the current temperature to determine the motor winding.

The runtime is itself a temperature-dependent variable based on the temperature-dependent permittivity of the dielectric of the pulse-conducting medium (here: measuring wire arrangement with insulation). By measuring the transit time of the introduced pulse, the temperature can therefore be determined via an evaluation.

In an advantageous embodiment of the invention it is provided that the measuring line is arranged along a stator section of the stator (preferably a stator tooth) in the region of a motor winding to be monitored. This has the advantage that, on the one hand, the stator tooth can be wound with the measuring line analogously to the actual motor winding, and furthermore the measurement takes place directly in the area of the motor winding, the temperature of which is to be recorded.

In a further advantageous embodiment of the invention, it is provided that the end of the measuring line is terminated or designed with a terminating resistor. The terminating resistor is the technical design of a high-frequency resistor, which, for. B. for measuring purposes or to avoid reflections as a load at the end of a line. Terminating resistors should have a particularly low induction design, which is why ground resistors are also used. In this respect, the end of the measuring line can be connected directly to a stator tooth carrying the motor winding to be monitored, which then acts as a terminating resistor.

It is also advantageous if the measuring line was first wound around a stator tooth, with which the motor winding is later wound. The measuring line is therefore inside the motor winding and can be wound around the stator tooth using the same winding method or winding technology as the motor winding, which has manufacturing and economic advantages.

It is also advantageously provided that a minimum permissible running time tmin is predetermined (and preferably stored permanently) and the evaluation unit disconnects the voltage supply from the motor or falls below this running time tmin or reduces the current consumption to a correspondingly lower value. This can e.g. B. at a pulse speed of less than 1/100 of the speed of light. A corresponding runtime can be defined as a limit value for the length of the relevant measuring section.

mit den folgenden Größen:

L*:

der induktive Leitungsbelag

C*:

der kapazitive Leitungsbelag

ε_r:

relative Permitivität

ε₀:

elektrische Feldkonstante

µ_r:

relative Permeabilität

µ₀:

magnetische Feldkonstante.

In a particularly advantageous embodiment of the invention, it is provided that the transit time of the pulse is determined by means of a computing operator from the pulse speed, which is dependent on the permittivity, for a known measuring line length, based on the following function with the evaluation unit: $$\nu \left(\vartheta \right)=\frac{1}{\sqrt{L*\cdot \mathrm{C.}*}}=\frac{1}{\sqrt{\mu \cdot \epsilon \left(\vartheta \right)}}=\frac{1}{\sqrt{{\mathrm{<figure-callout\; id="0"\; label="\mu "\; filenames="DE102018133282A1\_0004.png"\; state="\{\{state\}\}">\mu </figure-callout>}}_0\cdot {\mu }_r\cdot {\mathrm{<figure-callout\; id="0"\; label="\epsilon "\; filenames="DE102018133282A1\_0004.png"\; state="\{\{state\}\}">\epsilon </figure-callout>}}_0\cdot {\epsilon }_r\left(\vartheta \right)}}=\frac{1}{\underset{c}{\underbrace{\sqrt{{\mathrm{<figure-callout\; id="0"\; label="\mu "\; filenames="DE102018133282A1\_0004.png"\; state="\{\{state\}\}">\mu </figure-callout>}}_0\cdot {\epsilon }_0}}}}\cdot \frac{1}{\sqrt{{\mu }_r\cdot {\epsilon }_r\left(\vartheta \right)}}$$

with the following sizes:

L *:

the inductive cable covering

C *:

the capacitive cable covering

ε _r :

relative permittivity

ε ₀ :

electrical field constant

µ _r :

relative permeability

µ ₀ :

magnetic field constant.

In a first approximation, values between 1/50 and 1/100 of the speed of light c result from the following approximation equation for an exemplary insulator (here barium titanate): $$\nu \left(\vartheta \right)=c\cdot \frac{1}{\sqrt{\mathrm{3rd}\cdot {10}^{\mathrm{3rd}}...{10}^{\mathrm{4th}}}}\approx \frac{\mathrm{<figure-callout\; id="50"\; label="c"\; filenames="DE102018133282A1\_0004.png"\; state="\{\{state\}\}">c</figure-callout>}}{50}\cdots \frac{c}{100}$$

In the 3rd The description of preferred exemplary embodiments shows the functional relationship of the dielectric constant to the temperature.

In a preferred embodiment it is provided that the stator teeth of the electric motor, each of which is wound with a motor winding, are provided with a barium titanate layer (BaTiO3 coating).

1. a. Erzeugen eines Impulses mittels der Signalerzeugungseinrichtung und Einkopplung des Impulses in die Messleitung,
2. b. Erfassen der Impulslaufzeit des Impulses in der Messeleitung,
3. c. Bestimmen der aktuellen Temperatur der Motorwicklung mittels der Auswerteeinheit aus der Signallaufzeit.

Another aspect of the present invention relates to a method for monitoring the temperature of at least one (but preferably all) motor windings of an electric motor as described above, which comprises the following steps:

1. a. Generating a pulse by means of the signal generating device and coupling the pulse into the measuring line,
2. b. Detection of the pulse transit time of the pulse in the exhibition line,
3. c. Determining the current temperature of the motor winding using the evaluation unit from the signal runtime.

It is advantageous if a current flow through the motor windings is interrupted or reduced or the power supply to the motor is completely disconnected when a limit temperature is reached, namely when the temperature falls below a predefined pulse duration, preferably when the temperature falls below one hundredth.

Other advantageous developments of the invention are characterized in the subclaims or are shown in more detail below together with the description of the preferred embodiment of the invention with reference to the figures.

• 1 eine schematische Prinzipskizze zur Erläuterung der Erfindung,
• 2 ein Detail aus der 1, die einen exemplarischen Statorzahn mit einer Messleitung zeigt und
• 3 zeigt den funktionalen Zusammenhang der Dielektrizitätskonstante von Bariumtitanat (BaTio3) zur Temperatur.

Show it:

• 1 1 shows a schematic diagram to explain the invention,
• 2nd a detail from the 1 which shows an exemplary stator tooth with a measuring line and
• 3rd shows the functional relationship of the dielectric constant of barium titanate (BaTio3) to the temperature.

In 1 is an electric motor in a schematic representation with a stator 1 with motor windings 2nd and with a temperature monitoring device 10 shown. The temperature monitor 10 has to monitor the temperature of the respective motor windings 2nd via a respective measuring line 20 that are in the area of the respective motor winding 2nd is arranged as in the detail of the 2nd can be seen.

In the detail of the 2nd is the measuring line 20 around a stator tooth 11 wrapped around underneath the actual motor winding. This means that the test lead is wound around the tooth on a barium titanate layer. The measuring line 20 extends from a connector 21st for coupling an electromagnetic pulse or signal to the end of a test lead 22 on which a terminating resistor 23 is appropriate.

The temperature monitor 10 also has a signal generating device 30th for generating an electromagnetic pulse or signal and via a measuring device 40 for measuring the signal propagation time in the measuring line 20 .

In addition, there is an evaluation unit 50 provided that the current temperature of the respective motor winding is formed from the signal transit time that is currently being recorded 2nd to determine.

In the exemplary embodiment shown, the stator tooth is coated B made of barium titanate (BaTiO3) coated. The 3rd shows the functional relationship of the dielectric constant of barium titanate (BaTio3) to the temperature. This shows a significant increase in permittivity in the range around 120 ° C. If the winding temperature and thus the temperature of the barium titanate comes close to 120 ° C, the pulse speed changes from approx. C / 50 to approx. C / 100, which can be measured with a conventional measuring device for measuring pulse transit times.

The embodiment of the invention is not limited to the preferred exemplary embodiments specified above. Rather, a number of variants are conceivable which make use of the solution explained, even in the case of fundamentally different types.

Claims (11)

Electric motor with a stator (1) with motor windings (2) and with a temperature monitoring device (10) for monitoring the temperature of at least one motor winding, the temperature monitoring device (10) having a measuring line (20) in the area of the motor winding, which extends from a connection ( 21) for coupling an electromagnetic pulse or signal up to a measuring line end (22), the temperature monitoring device (10) having a signal generating device (30) for generating an electromagnetic pulse or signal and a measuring device (40) for measuring the signal transit time in the measuring line (20), as well as an evaluation unit (50), which is designed to determine the current temperature of the motor winding from the signal transit time currently being recorded. Electric motor with a temperature monitoring device according to Claim 1 , characterized in that the measuring line (20) is arranged along a stator section of the stator (1) in the region of a motor winding (2) to be monitored. Electric motor with a temperature monitoring device according to Claim 1 or 2nd , characterized in that in each case a measuring line (20) is arranged along a stator section of the stator (1) in the region of each motor winding (2) to be monitored. Electric motor according to one of the preceding Claims 1 to 3rd , characterized in that the measuring line end (22) is formed with a terminating resistor (23). Electric motor according to one of the preceding Claims 1 to 3rd , characterized in that the measuring line end (22) is directly connected to a stator tooth (11) carrying the motor winding (2) to be monitored. Electric motor according to one of the preceding claims, characterized in that the measuring line (20) is wound around a stator tooth (11) with which the motor winding (2) is wound. Electric motor according to one of the preceding claims, characterized in that a minimum permissible running time t _{min is} specified and the evaluation unit (50) disconnects the voltage supply from the motor when the running time t _{min is} undershot or reduces the current consumption to a correspondingly lower value. Electric motor according to one of the preceding claims, characterized in that the transit time of the pulse is determined by means of a computing operator from the pulse speed, which is dependent on the permittivity, for a known measuring line length, on the basis of the following function with the evaluation unit (40): $$\nu \left(\vartheta \right)=\frac{1}{\sqrt{L*\cdot \mathrm{C.}*}}=\frac{1}{\sqrt{\mu \cdot \epsilon \left(\vartheta \right)}}=\frac{1}{\sqrt{{\mu }_0\cdot {\mu }_r\cdot {\epsilon }_0\cdot {\epsilon }_r\left(\vartheta \right)}}=\frac{1}{\underset{c}{\underbrace{\sqrt{{\mu }_0\cdot {\epsilon }_0}}}}\cdot \frac{1}{\sqrt{{\mu }_r\cdot {\epsilon }_r\left(\vartheta \right)}}$$

with: L *: the inductive cable covering C *: the capacitive cable covering ε _r : relative permittivity ε ₀ : electrical field constant µ _r : relative permeability µ ₀ : magnetic field constant Electric motor according to one of the preceding claims, characterized in that the stator teeth (11) of the electric motor each wrapped with a motor winding (2) are provided with a barium titanate layer B (BaTiO3 coating). Method for monitoring the temperature of at least one motor winding of an electric motor according to one of the Claims 1 to 9 which comprises the following steps: a. Generating a pulse by means of the signal generating device (30) and coupling the pulse into the measuring line (20), b. Detecting the pulse transit time of the pulse in the measurement line (20), c. Determining the current temperature of the motor winding using the evaluation unit (50) from the signal runtime. Procedure according to Claim 10 , When a limit temperature is reached when falling below a predefined pulse transit time, preferably when falling below one hundredth of the speed of light, a current flow through the motor windings (2) is interrupted or reduced or the voltage supply to the motor is disconnected.

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